Check valves are well known in the art and have been built for centuries. In mechanical engineering practice, a check valve takes several forms. "Lift" or "poppet" check valves are characterized by containing a valve element that is located in the flow stream. In this type of valve, the force of the flow stream moves the valve element into an enlarged section of the flow duct so that the flow stream passes around the element with a minimum of turbulence. "Swing" check valves contain a valve element that is hinged to swing in the preferred direction of flow. Prior art valve elements having a generally flat configuration resulted in the requirement to change the cross-section of the flow duct for a considerable distant upstream and downstream from the valve location to minimize flow turbulence. These types of check valves are used extensively in process industries. In aircraft, the most commonly used check valve is the "flapper" check valve in which two semi-circular valve elements swing from a support in the center of the valve. These valves are commonly used in aircraft as they are more compact and are of lighter weight than any of the previously mentioned types.
The primary disadvantage of the prior art check valves is that significant pressure drops occur as a result of the protuberances, which are part of these valves, projecting the duct. Prior art "lift" and "flapper" check valves contain structure which protrudes into the highest velocity section of the flow. The prior art "swing" check valve requires that the duct cross-section be modified. In addition to pressure drop, these difficulties result in noise, weight, expended energy and the requirement of additional installation length in the duct.
The present invention, because of the shape of the closure element and because it swings to a position that maintains the circular cross-section of the duct when in the open position, results in a minimum pressure drop and minimizes the associated problems of noise and energy loss. Because the valve operates solely within the confines of the duct, the problems associated with the valve installation length are mitigated.
In order to maintain the circular cross-section of the duct, the present invention includes an elongated closure element formed in the shape of the circular wall of the duct. The closure element is hingedly connected to the duct wall at a point on an end edge of the element. When the valve is open, the circular cross-section of the inside diameter of the duct is maintained. The entire closure element operates solely within the confines of the duct to check the flow of material.
The geometry of the closure element of the valve is best understood by considering the surface formed by intersecting two cylinders within the inside radius of the duct. The angle of the wall of the closure element in the closed position with respect to the primary duct is the angle between two cylinders whose center lines intersect at an angle .THETA.. Modifications are made to the geometry to prevent the lower corners of the closure element from intersecting the duct wall during rotation. In theory, this curved surface results in small sectors of open area between the closure element and the duct wall on each side of the closure element when the valve is in the closed position. In practice, this area is small and in many instances may be ignored. It may be minimized by adding small flats to the duct on each side. As these flats are at the duct wall where the velocity is lowest and the effect on pressure drop is negligible.
The surface at the outer edge of the closure element will be defined by a curve which is generated by sweeping the curves that limit the surface at the inside radius of the duct about the hinge point.